Use of Ca(NO3)2 for EI

KNO3 has been restricted here in Singapore and only holders of permits are allowed to purchase KNO3 in its dry form (only 5% concentration is allowed to be sold to the public). I've tried switching to commercial brands of ferts, but it's not cost efficient and I'm not getting the same results that I was when using EI. Recently, I've stumbled upon the use of Ca(NO3)2 in EI. I've made some enquiries and should be able to get some (1kg) in December.

As Ca(NO3)2 is hygroscopic, I've decided to make a batch of liquid "Macro" ferts to avoid having a messy sludge after some time if I were to dose it dry. My tank is a 4x2x2 ft 120 gal tank, and using APC's calculator, I need 1 teaspoon (5g) of Ca(NO3)2 per dose to get 8+ppm. This is similar to the 1.5 teaspoons of KNO3 recommended by EI for dummies.

A few questions that arise from this are:

1. I've done some preliminary research and found that 38g/100ml of Ca(NO3)2/water is saturation level. I've calculated that if I mix in 25g/100ml of water, I can dose 20ml of the liquid to get the 8+ppm. As I'm getting 1kg of the chemical, will there be any issue if I were to mix up 4 litres at once and store it to be used over about a year? Of course i'd shake the bottles vigorously to make sure it's all dissolved before dosing

2. For ease of dosing, can I mix in other dry ferts to this solution? I'm looking at K2SO4 and MgSO4 to supply K and Mg respectively. I've been told KH2PO4 cannot be mixed in and has to be dosed separately or an insoluble precipitate would be formed and would be useless to the plants. The reason for dosing MgSO4 is that I'm already going to be getting Ca from the Ca(NO3)2 and K from the KH2PO4 + K2SO4. Hence, dosing MgSO4 means I can bypass the weekly Seachem Equilibrium dose.

3. If I can indeed mix up those 3 ferts into 1 solution, would I have to reduce the concentration of Ca(NO3)2 to ensure that the other 2 ferts can dissolve? I have forgotten all my basic chemistry!

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